path: root/doc/editcap.pod

=head1 NAME

editcap - Edit and/or translate the format of capture files

=head1 SYNOPSIS

B<editcap>
S<[ B<-a> E<lt>frame:commentE<gt> ]>
S<[ B<-A> E<lt>start timeE<gt> ]>
S<[ B<-B> E<lt>stop timeE<gt> ]>
S<[ B<-c> E<lt>packets per fileE<gt> ]>
S<[ B<-C> [offset:]E<lt>choplenE<gt> ]>
S<[ B<-E> E<lt>error probabilityE<gt> ]>
S<[ B<-F> E<lt>file formatE<gt> ]>
S<[ B<-h> ]>
S<[ B<-i> E<lt>seconds per fileE<gt> ]>
S<[ B<-o> E<lt>change offsetE<gt> ]>
S<[ B<-L> ]>
S<[ B<-r> ]>
S<[ B<-s> E<lt>snaplenE<gt> ]>
S<[ B<-S> E<lt>strict time adjustmentE<gt> ]>
S<[ B<-t> E<lt>time adjustmentE<gt> ]>
S<[ B<-T> E<lt>encapsulation typeE<gt> ]>
S<[ B<-v> ]>
I<infile>
I<outfile>
S<[ I<packet#>[-I<packet#>] ... ]>

B<editcap>
S< B<-d> > |
S< B<-D> E<lt>dup windowE<gt> > |
S< B<-w> E<lt>dup time windowE<gt> >
S<[ B<-v> ]>
S<[ B<-I> E<lt>bytes to ignoreE<gt> ]>
I<infile>
I<outfile>

B<editcap>
S<[ B<-V> ]>

=head1 DESCRIPTION

B<Editcap> is a program that reads some or all of the captured packets from the
I<infile>, optionally converts them in various ways and writes the
resulting packets to the capture I<outfile> (or outfiles).

By default, it reads all packets from the I<infile> and writes them to the
I<outfile> in pcap file format.

An optional list of packet numbers can be specified on the command tail;
individual packet numbers separated by whitespace and/or ranges of packet
numbers can be specified as I<start>-I<end>, referring to all packets from
I<start> to I<end>.  By default the selected packets with those numbers will
I<not> be written to the capture file.  If the B<-r> flag is specified, the
whole packet selection is reversed; in that case I<only> the selected packets
will be written to the capture file.

B<Editcap> can also be used to remove duplicate packets.  Several different
options (B<-d>, B<-D> and B<-w>) are used to control the packet window
or relative time window to be used for duplicate comparison.

B<Editcap> can be used to assign comment strings to frame numbers.

B<Editcap> is able to detect, read and write the same capture files that
are supported by B<Wireshark>.
The input file doesn't need a specific filename extension; the file
format and an optional gzip compression will be automatically detected.
Near the beginning of the DESCRIPTION section of wireshark(1) or
L<https://www.wireshark.org/docs/man-pages/wireshark.html>
is a detailed description of the way B<Wireshark> handles this, which is
the same way B<Editcap> handles this.

B<Editcap> can write the file in several output formats. The B<-F>
flag can be used to specify the format in which to write the capture
file; B<editcap -F> provides a list of the available output formats.

=head1 OPTIONS

=over 4

=item -a  E<lt>framenum:commentE<gt>

For the specificed frame number, assign the given comment string.
Can be repeated for multiple frames.  Quotes should be used with comment
strings that include spaces.

=item -A  E<lt>start timeE<gt>

Saves only the packets whose timestamp is on or after start time.
The time is given in the following format YYYY-MM-DD HH:MM:SS

=item -B  E<lt>stop timeE<gt>

Saves only the packets whose timestamp is before stop time.
The time is given in the following format YYYY-MM-DD HH:MM:SS

=item -c  E<lt>packets per fileE<gt>

Splits the packet output to different files based on uniform packet counts
with a maximum of <packets per file> each. Each output file will
be created with a suffix -nnnnn, starting with 00000. If the specified
number of packets is written to the output file, the next output file is
opened. The default is to use a single output file.

=item -C  [offset:]E<lt>choplenE<gt>

Sets the chop length to use when writing the packet data. Each packet is
chopped by <choplen> bytes of data. Positive values chop at the packet
beginning while negative values chop at the packet end.

If an optional offset precedes the <choplen>, then the bytes chopped will be
offset from that value. Positive offsets are from the packet beginning, while
negative offsets are from the packet end.

This is useful for chopping headers for decapsulation of an entire capture,
removing tunneling headers, or in the rare case that the conversion between two
file formats leaves some random bytes at the end of each packet. Another use is
for removing vlan tags.

NOTE: This option can be used more than once, effectively allowing you to chop
bytes from up to two different areas of a packet in a single pass provided that
you specify at least one chop length as a positive value and at least one as a
negative value.  All positive chop lengths are added together as are all
negative chop lengths.

=item -d

Attempts to remove duplicate packets.  The length and MD5 hash of the
current packet are compared to the previous four (4) packets.  If a
match is found, the current packet is skipped.  This option is equivalent
to using the option B<-D 5>.

=item -D  E<lt>dup windowE<gt>

Attempts to remove duplicate packets.  The length and MD5 hash of the
current packet are compared to the previous <dup window> - 1 packets.
If a match is found, the current packet is skipped.

The use of the option B<-D 0> combined with the B<-v> option is useful
in that each packet's Packet number, Len and MD5 Hash will be printed
to standard out.  This verbose output (specifically the MD5 hash strings)
can be useful in scripts to identify duplicate packets across trace
files.

The <dup window> is specified as an integer value between 0 and 1000000 (inclusive).

NOTE: Specifying large <dup window> values with large tracefiles can
result in very long processing times for B<editcap>.

=item -E  E<lt>error probabilityE<gt>

Sets the probability that bytes in the output file are randomly changed.
B<Editcap> uses that probability (between 0.0 and 1.0 inclusive)
to apply errors to each data byte in the file.  For instance, a
probability of 0.02 means that each byte has a 2% chance of having an error.

This option is meant to be used for fuzz-testing protocol dissectors.

=item -F  E<lt>file formatE<gt>

Sets the file format of the output capture file.
B<Editcap> can write the file in several formats, B<editcap -F>
provides a list of the available output formats. The default
is the B<pcap> format.

=item -h

Prints the version and options and exits.

=item -i  E<lt>seconds per fileE<gt>

Splits the packet output to different files based on uniform time intervals
using a maximum interval of <seconds per file> each. Each output file will
be created with a suffix -nnnnn, starting with 00000. If packets for the specified
time interval are written to the output file, the next output file is
opened. The default is to use a single output file.

=item -I  E<lt>bytes to ignoreE<gt>

Ignore the specified bytes number at the beginning of the frame during MD5 hash calculation
Useful to remove duplicated packets taken on several routers(differents mac addresses for example)
e.g. -I 26 in case of Ether/IP/ will ignore ether(14) and IP header(20 - 4(src ip) - 4(dst ip)).
The default value is 0.

=item -L

Adjust the original frame length accordingly when chopping and/or snapping
(in addition to the captured length, which is always adjusted regardless of
whether B<-L> is specified or not).  See also B<-C <choplen>> and B<-s <snaplen>>.

=item -o  E<lt>change offsetE<gt>

When used in conjuction with -E, skip some bytes from the beginning of the packet
from being changed. In this way some headers don't get changed, and the fuzzer is
more focused on a smaller part of the packet. Keeping a part of the packet fixed
the same dissector is triggered, that make the fuzzing more precise.

=item -r

Reverse the packet selection.
Causes the packets whose packet numbers are specified on the command
line to be written to the output capture file, instead of discarding them.

=item -s  E<lt>snaplenE<gt>

Sets the snapshot length to use when writing the data.
If the B<-s> flag is used to specify a snapshot length, packets in the
input file with more captured data than the specified snapshot length
will have only the amount of data specified by the snapshot length
written to the output file.

This may be useful if the program that is
to read the output file cannot handle packets larger than a certain size
(for example, the versions of snoop in Solaris 2.5.1 and Solaris 2.6
appear to reject Ethernet packets larger than the standard Ethernet MTU,
making them incapable of handling gigabit Ethernet captures if jumbo
packets were used).

=item -S  E<lt>strict time adjustmentE<gt>

Time adjust selected packets to ensure strict chronological order.

The <strict time adjustment> value represents relative seconds
specified as [-]I<seconds>[I<.fractional seconds>].

As the capture file is processed each packet's absolute time is
I<possibly> adjusted to be equal to or greater than the previous
packet's absolute timestamp depending on the <strict time
adjustment> value.

If <strict time adjustment> value is 0 or greater (e.g. 0.000001)
then B<only> packets with a timestamp less than the previous packet
will adjusted.  The adjusted timestamp value will be set to be
equal to the timestamp value of the previous packet plus the value
of the <strict time adjustment> value.  A <strict time adjustment>
value of 0 will adjust the minimum number of timestamp values
necessary to ensure that the resulting capture file is in
strict chronological order.

If <strict time adjustment> value is specified as a
negative value, then the timestamp values of B<all>
packets will be adjusted to be equal to the timestamp value
of the previous packet plus the absolute value of the
<lt>strict time adjustment<gt> value. A <strict time
adjustment> value of -0 will result in all packets
having the timestamp value of the first packet.

This feature is useful when the trace file has an occasional
packet with a negative delta time relative to the previous
packet.

=item -t  E<lt>time adjustmentE<gt>

Sets the time adjustment to use on selected packets.
If the B<-t> flag is used to specify a time adjustment, the specified
adjustment will be applied to all selected packets in the capture file.
The adjustment is specified as [-]I<seconds>[I<.fractional seconds>].
For example, B<-t> 3600 advances the timestamp on selected packets by one
hour while B<-t> -0.5 reduces the timestamp on selected packets by
one-half second.

This feature is useful when synchronizing dumps
collected on different machines where the time difference between the
two machines is known or can be estimated.

=item -T  E<lt>encapsulation typeE<gt>

Sets the packet encapsulation type of the output capture file.
If the B<-T> flag is used to specify an encapsulation type, the
encapsulation type of the output capture file will be forced to the
specified type.
B<editcap -T> provides a list of the available types. The default
type is the one appropriate to the encapsulation type of the input
capture file.

Note: this merely
forces the encapsulation type of the output file to be the specified
type; the packet headers of the packets will not be translated from the
encapsulation type of the input capture file to the specified
encapsulation type (for example, it will not translate an Ethernet
capture to an FDDI capture if an Ethernet capture is read and 'B<-T
fddi>' is specified). If you need to remove/add headers from/to a
packet, you will need od(1)/text2pcap(1).

=item -v

Causes B<editcap> to print verbose messages while it's working.

Use of B<-v> with the de-duplication switches of B<-d>, B<-D> or B<-w>
will cause all MD5 hashes to be printed whether the packet is skipped
or not.

=item -V

Print the version and exit.

=item -w  E<lt>dup time windowE<gt>

Attempts to remove duplicate packets.  The current packet's arrival time
is compared with up to 1000000 previous packets.  If the packet's relative
arrival time is I<less than or equal to> the <dup time window> of a previous packet
and the packet length and MD5 hash of the current packet are the same then
the packet to skipped.  The duplicate comparison test stops when
the current packet's relative arrival time is greater than <dup time window>.

The <dup time window> is specified as I<seconds>[I<.fractional seconds>].

The [.fractional seconds] component can be specified to nine (9) decimal
places (billionths of a second) but most typical trace files have resolution
to six (6) decimal places (millionths of a second).

NOTE: Specifying large <dup time window> values with large tracefiles can
result in very long processing times for B<editcap>.

NOTE: The B<-w> option assumes that the packets are in chronological order.
If the packets are NOT in chronological order then the B<-w> duplication
removal option may not identify some duplicates.

=back

=head1 EXAMPLES

To see more detailed description of the options use:

    editcap -h

To shrink the capture file by truncating the packets at 64 bytes and writing it as Sun snoop file use:

    editcap -s 64 -F snoop capture.pcap shortcapture.snoop

To delete packet 1000 from the capture file use:

    editcap capture.pcap sans1000.pcap 1000

To limit a capture file to packets from number 200 to 750 (inclusive) use:

    editcap -r capture.pcap small.pcap 200-750

To get all packets from number 1-500 (inclusive) use:

    editcap -r capture.pcap first500.pcap 1-500

or

    editcap capture.pcap first500.pcap 501-9999999

To exclude packets 1, 5, 10 to 20 and 30 to 40 from the new file use:

    editcap capture.pcap exclude.pcap 1 5 10-20 30-40

To select just packets 1, 5, 10 to 20 and 30 to 40 for the new file use:

    editcap -r capture.pcap select.pcap 1 5 10-20 30-40

To remove duplicate packets seen within the prior four frames use:

    editcap -d capture.pcap dedup.pcap

To remove duplicate packets seen within the prior 100 frames use:

    editcap -D 101 capture.pcap dedup.pcap

To remove duplicate packets seen I<equal to or less than> 1/10th of a second:

    editcap -w 0.1 capture.pcap dedup.pcap

To display the MD5 hash for all of the packets (and NOT generate any
real output file):

    editcap -v -D 0 capture.pcap /dev/null

or on Windows systems

    editcap -v -D 0 capture.pcap NUL

To advance the timestamps of each packet forward by 3.0827 seconds:

    editcap -t 3.0827 capture.pcap adjusted.pcap

To ensure all timestamps are in strict chronological order:

    editcap -S 0 capture.pcap adjusted.pcap

To introduce 5% random errors in a capture file use:

    editcap -E 0.05 capture.pcap capture_error.pcap

To remove vlan tags from all packets within an Ethernet-encapsulated capture
file, use:

    editcap -L -C 12:4 capture_vlan.pcap capture_no_vlan.pcap

To chop both the 10 byte and 20 byte regions from the following 75 byte packet
in a single pass, use any of the 8 possible methods provided below:

    <--------------------------- 75 ---------------------------->

    +---+-------+-----------+---------------+-------------------+
    | 5 |   10  |     15    |       20      |         25        |
    +---+-------+-----------+---------------+-------------------+

    1) editcap -C 5:10 -C -25:-20 capture.pcap chopped.pcap
    2) editcap -C 5:10 -C 50:-20 capture.pcap chopped.pcap
    3) editcap -C -70:10 -C -25:-20 capture.pcap chopped.pcap
    4) editcap -C -70:10 -C 50:-20 capture.pcap chopped.pcap
    5) editcap -C 30:20 -C -60:-10 capture.pcap chopped.pcap
    6) editcap -C 30:20 -C 15:-10 capture.pcap chopped.pcap
    7) editcap -C -45:20 -C -60:-10 capture.pcap chopped.pcap
    8) editcap -C -45:20 -C 15:-10 capture.pcap chopped.pcap

To add comment strings to the first 2 input frames, use:

    editcap -a "1:1st frame" -a 2:Second capture.pcap capture-comments.pcap

=head1 SEE ALSO

pcap(3), wireshark(1), tshark(1), mergecap(1), dumpcap(1), capinfos(1),
text2pcap(1), od(1), pcap-filter(7) or tcpdump(8)

=head1 NOTES

B<Editcap> is part of the B<Wireshark> distribution.  The latest version
of B<Wireshark> can be found at L<https://www.wireshark.org>.

HTML versions of the Wireshark project man pages are available at:
L<https://www.wireshark.org/docs/man-pages>.

=head1 AUTHORS

  Original Author
  -------- ------
  Richard Sharpe           <sharpe[AT]ns.aus.com>


  Contributors
  ------------
  Guy Harris               <guy[AT]alum.mit.edu>
  Ulf Lamping              <ulf.lamping[AT]web.de>